In underground longwall mining, a plurality of pans are connected in an end-to-end, modular relationship to form a “face” conveyor for handling the mined minerals, such as coal. In addition to receiving the minerals won from the working face and guiding flights that convey the minerals away, the mating pans (collectively referred to as a “panline”) also serve as a guide track for the cutter/shearer as it reciprocates back and forth along the face. Using a system of rams or similar motive devices, the panline is continuously advanced forward in a sequential fashion as the cuts are made.
Typically, temporary hydraulic roof supports known as shields move along with and protect the shearer and face conveyor (collectively referred to as the longwall “miner” or “mining machine”). As these shields advance, the roof is usually allowed to collapse behind the miner. The exception is during the last few passes of the shearer, where the shields are not advanced in order to create a sufficiently large passageway to facilitate the time-consuming disassembly and relocation of the longwall miner. As a result, a relatively large area of unsupported roof may exist between the shields and the working face.
In this situation, it is desirable and in fact required by law to install a more permanent type of support at certain specified locations along the unsupported roof and ribs of the mine passage in an effort to prevent a deleterious collapse. Typically, the most efficient manner of providing such support involves using what is known in the vernacular as a “roof” bolt (even though it is equally effective in the “ribs” of the mine passage as well). In the usual case, the bolt comprises an elongated piece of metal (such as rebar) inserted in a borehole drilled in the corresponding face and held in place by a previously introduced quick-setting resin. The installed bolt thus anchors the exposed strata (usually the next-adjacent one) and provides the desired support for at least a portion of the adjacent face.
To meet the need for providing support for the roof adjacent to the working face, others in the past have proposed a special type of drilling/bolting unit for use in association with the panline of the face conveyor. This unit is adapted for traversing to and fro along the panline and carries an operator who installs the bolts along the newly formed roof and/or ribs using an onboard drill mast. One example of such a unit is found in U.S. Pat. No. 6,109,700 to Branson et al., the disclosure of which is incorporated herein by reference. The advantage of such a unit is that it dispenses with the need for moving a separate bolting machine (which is typically a relatively large vehicle on wheels or crawler tracks) into the confined space between the shields and the working face.
Although this type of unit works well for its intended purpose, it experiences a significant amount of downtime while the shearing operation progresses and the panline concomitantly advances toward the face during the longwall operation. During this period of non-use, other locations in the mine (including those where conventional (i.e., non-longwall) mining takes place) could benefit from the use of an extra or “utility” drilling/bolting unit. However, past panline drilling/bolting units, including the modern version shown in the '700 patent, have deleteriously not been adapted for use apart from the panline. Consequently, the mine operator must purchase a separate non-panline type drilling/bolting vehicle for drilling/bolting at remote locations while the panline unit sits dormant. This obviously increases not only the capital investment, but also the operating and maintenance costs associated with the mining operation. The end result is either higher market prices for the won minerals (which can be problematic in the highly competitive marketplace) or a decrease in profit for the mining operator.
Accordingly, a need is identified for a panline drilling or bolting unit adapted for use elsewhere in an underground mine and apart from the face conveyor.